Integrated gas dehydrator

ABSTRACT

The present invention related to an apparatus, in particular an integrated gas dehydrator, comprising an integrated dehydrator processing unit and a refrigeration unit for efficient and cost-effective removal of moisture in a variety of gases, in particular the natural gas.

BACKGROUND OF THE INVENTION

[0001] Refrigeration dehydration technology has been widely adopted in air dehumidification as well as in compressed air dehydration. Most recently, this technology has also been developed for the dehydration of natural gas (abbreviated as NG hereafter) and other process gases. The 1997 U.S. Pat. No. 5,664,426, “Regenerative Gas Dehydrator,” provided the basis for the application of refrigeration dehydration method to the NG industry. Following a successful field test Mid-2000 at an NG well in Texas, the commercialization of such a technology is now underway. An important improvement related to the said technology was proposed in 1999, and was granted a U.S. Pat. No. 6,158,242, “Gas Dehydration Method and Apparatus,” in December 2000. A similar patent application was also filed in the PRC, where substantial R&D efforts on refrigeration dehydration have been carried out.

[0002] Presently all the commercial products of the refrigeration dehydrators comprise the following four major components:1. The refrigerator, i.e., a cooling source for providing refrigeration to the said gas dehydrator;2. The chiller, or freezer, i.e., a heat exchanger for cooling the gas to the required dew-point so as to remove the moisture from the gas;3. The pre-cooler, or so-called “regenerator,” i.e., another heat exchanger for pre-cooling the inlet gas by recycling the cold dehydrated gas, and removing a portion of the moisture from the gas; and 4. The gas-liquid/solid particles separator for separating the liquid or solid particles entrained in the gas stream exiting from the chiller.

[0003] The above four components are usually installed separately and interconnected with pipelines. As a consequence, the dehydrator system is rather complex and bulky. When solid ice and/or gas hydrates appear in the dehydration system, the operations will become cumbersome.

[0004] During the past two decades, a lot of efforts have been made in improving the refrigeration dehydrators on the market. A number of patents have been granted in this area, notably the U.S. Pat. Nos. 4,638,852 (1987), 4,761,968 (1988), and 5,107,919 (1992). These improvements, however, mostly focused on the enhancement of the performance of the individual components, e.g., heat exchangers.

[0005] They did not overcome the above-mentioned major drawbacks, and, hence could not mitigate the clogging problems caused by the appearance of solid ice and/or gas hydrate deposits in the refrigeration dehydrators, in particular, inside the interconnection pipelines and the respective inlets and outlets.

[0006] Accordingly, it is an objective of the present invention to provide an integrated gas dehydrator comprising only two components, i.e., a single integrated dehydrator processing unit and a refrigeration unit. The said integrated dehydrator processing unit comprises three elements in a single piece of equipment, i.e., the chiller, the pre-cooler, and the separator. No interconnecting pipeline among those elements is required. As a consequence, the clogging problems caused by the appearance of solid ice and/or gas hydrate deposits inside the interconnecting pipelines and the respective inlets and outlets are eliminated.

[0007] A further objective of the present invention is to provide a highly efficient, compact, and cost-effective integrated NG dehydrator not only applicable to terrestrial NG sites but also applicable to the off-shore NG platforms.

SUMMARY OF THE INVENTION

[0008] With regard to the above and other objectives, the present invention provides an integrated gas dehydrator comprising a single integrated dehydrator processing unit and a refrigeration unit (hereafter abbreviated as “refrigerator”) for efficient and cost-effective removal of moisture in a variety of gases, in particular the NG.

[0009] The said integrated dehydrator processing unit comprises the following sections: a pre-cooler, a transition section, and a chiller, with gas-liquid/solid particle separators inserted between these sections, as appropriate. When incorporated with a refrigerator, the said single piece dehydrator processing unit could perform the entire gas dehydration processes.

[0010] The refrigerator provides the cooling medium required by the said integrated dehydrator processing unit. The refrigerator may be a industrial refrigeration unit, or, alternatively, a gas expander/compressor unit as appropriate.

[0011] The principle of the operations of the integrated gas dehydrator follows.

[0012] The moisture-laden inlet gas, while flowing in the primary side of the pre-cooler, is cooled down to a temperature as close to the desired dew-point as practical by the cold dehydrated gas reflux. A substantial portion of the moisture of the inlet gas is condensed into liquid water and/or frozen as solid ice/gas hydrates. The majority of the condensates and/or solids are deposited on the surface of the gas-flow channels, but a small portion is entrained in the gas stream as tinny droplets and/or particles. The entrained droplets and/or particles are separated with appropriate means in a separator incorporated between the pre-cooler and the transition section. When exited from the separator, the pre-cooled and partially dehydrated gas enters the primary side of the transition section, wherein the secondary side is empty, without any coolant. Due to heat conduction along the metal walls, a portion of the residual moisture in the gas is further frozen on the surface of the gas flow channels. The entrained particles are separated in the second separator. The gas then enters the primary side of the chiller wherein the gas is deep-cooled by the refrigerant flowing in the secondary side of the chiller. The gas is rapidly cooled down in the chiller to the desired dew-point and is dehydrated to the required low level. When eventually exited from the final separator, the cold, dehydrated gas is recycled as a reflux to the secondary side of the pre-cooler to cool the inlet gas.

[0013] When the pressure of the inlet gas is sufficiently high, the required refrigeration could be provided with expanding the cold dehydrated gas in a gas expander/compressor. In such a case, no external energy is required for refrigeration.

BRIEF DESCRIPTION OF DRAWINGS

[0014] The above and other features and advantages of the present invention will now be further described in the following detailed descriptions in conjunction with the attached drawings in which:

[0015]FIG. 1 illustrates one preferred embodiment of the integrated dehydrator processing unit wherein a pre-cooler, a transition section, and a chiller are arranged in tandem, i.e., in an end-to-end configuration;

[0016]FIG. 2 illustrates a different embodiment of the integrated dehydrator processing unit wherein a pair of pre-coolers, a pair of transition sections, and a central chiller are arranged in a side-by-side configuration; and

[0017]FIG. 3 illustrates another preferred embodiment of the integrated dehydrator processing unit wherein a pre-cooler comprising a multiplicity (two in this figure as example) of sub-sections is arranged in tandem, i.e., in an end-to-end configuration of sub-sections, with a transition section and a chiller.

DETAILED DESCRIPTION

[0018]FIG. 1 illustrates one preferred embodiment of the integrated dehydrator processing unit wherein a pre-cooler, a transition section, and a chiller are arranged in tandem, i.e., in an end-to-end configuration.

[0019] The said integrated dehydrator processing unit could be constructed as a special high-efficiency heat exchanger, for example, a multi-sectional finned-plate heat exchanger. The three major sections in FIG. 1 are designated respectively as the precooler 2, the transition section 6, and the chiller 7, being arranged in tandem. The first gas-liquid/solid particle separator 5 a is incorporated between the pre-cooler 2 and the transition section 6. The second gas-liquid/solid particle separator 5 b is incorporated between the transition section 6 and the chiller 7. The third or final liquid/solid particle-gas separator 5 c is incorporated at the exit end of the chiller 7. Four water discharge pipes, 4 a, 4 b, 4 c, and 4 d are connected respectively to the bottom of the gas inlet 1, and to the first, second, and third separators 5 a, 5 b, and 5 c.

[0020] A reflux pipeline 51 connects the final separator 5 c and the top of the secondary side of the pre-cooler 2. The dehydrated gas outlet 10 is connected to the bottom of the secondary side of the pre-cooler 2.

[0021] The refrigerant enters and exits from the chiller via the refrigerant inlet 8 and the refrigerant outlet 9, respectively. The refrigerant is provided either with an industrial refrigeration unit, or a gas expander/compressor unit, as appropriate; both of which are not shown in FIG. 1.

[0022] The operations of the integrated gas dehydrator follow. The moisture-laden inlet gas enters the primary side of the pre-cooler 2 via the gas inlet 1 and flows upward. The gas is cooled down to a temperature as close to the desired dew-point as practical with the cold dehydrated gas reflux. The cold reflux gas enters the secondary side of the pre-cooler 2 via the reflux inlet 3 and exits via the gas outlet 1 0. A substantial portion of the moisture of the inlet gas is condensed into liquid water and/or frozen as solid ice/gas hydrates. The majority of the condensates and/or solids are deposited on the surface of the gas-flow channels. A small portion of the condensates or solids is entrained in the gas stream in the form of tinny droplets or particles. The droplets/particles are separated from the gas in the first separator 5 a. The exiting temperature of the pre-cooled gas is generally below the freezing point of water.

[0023] The pre-cooled and partially dehydrated gas then enters the primary side of the transition section 6 wherein the secondary side is empty, i.e., without any coolant. Heat conduction along the metal walls in the gas flow direction is the only mechanism for further cooling down the inlet gas. Under such a condition, the temperature drop across the heat exchange surface is relatively small, and the accumulation rate of the solid ice/gas hydrates on the surface of the gas-flow channels is reduced. The solid particles entrained in the gas are separated in the second separator 5 b.

[0024] The partially dehydrated cold gas then enters the primary side of the chiller 7 wherein it is deep-cooled by the refrigerant entering the secondary side via the refrigerant inlet 8 and exiting via the refrigerant outlet 9. In the chiller 7, the gas is rapidly cooled down to the desired dew-point, and is dehydrated to the required low level. When exited from the third (final) separator 5 c, the cold dehydrated gas is recycled via the reflux pipeline 51 to the top of the secondary side of the pre-cooler 2 for cooling the inlet gas. The dehydrated gas eventually leaves the integrated dehydrator processing unit via the gas outlet 10.

[0025]FIG. 2 illustrates a different embodiment of the integrated dehydrator processing unit wherein a pair of pre-coolers, a pair of transition sections, and a central chiller are arranged in a side-by-side configuration.

[0026] The said integrated dehydrator processing unit comprises the following sections arranged in a symmetrical side-by-side configuration: a pair of pre-coolers 2 and 2 a, a pair of transition sections 6 and 6 a, and one central chiller 7. The liquid/solid particle-gas separators 5/5 a are incorporated respectively between the pair of pre-coolers 2/2 a and the pair of transition sections 6/6 a. A common second gas-liquid/solid particle separator 5 b is incorporated between the pair of transition sections 6/6 a and the central section 7. The third gas-liquid/solid particle separator 5 c is incorporated between the central chiller 7 and the pair of pre-coolers 2/2 a. Three water discharge pipes, 4 a, 4 b, and 4 c are connected respectively to the separators 5 a, 5 b, and 5 c. Two reflux gas openings 51/51 a connect the third separator 5 c to the bottom of the secondary side of the pre-coolers 2/2 a, respectively. Two gas outlets 10/10 a are connected to the top of the secondary side of the pre-cooler 2/2 a, respectively. Two gas inlets 1/1 a are connected to the top of the primary side of the pre-cooler 2/2 a, respectively. The refrigerant enters the chiller via the refrigerant inlet 8 and exits from the refrigerant outlet 9. The refrigerant is provided with an industrial refrigeration unit, or, alternatively, with a gas expander/compressor unit, as appropriate; both of which are not shown in FIG. 2.

[0027] The operations of this dehydrator in FIG. 2 are identical to that already described in FIG. 1. The flow paths of the gas and the refrigerant are shown by the respective dotted lines with arrows indicting the directions of the flows. Since the dehydration process are identical with that described in FIG. 1, no further detailed description needs to be repeated.

[0028]FIG. 3 illustrates another preferred embodiment of the integrated dehydrator processing unit wherein a pre-cooler comprising a multiplicity (two in this figure, for example) of sub-sections is arranged in tandem, i.e., in an end-to-end configuration, with a transition section and a chiller.

[0029] The integrated dehydrator processing unit in FIG. 3 is quite similar to that described in FIG. 1, with the only exception that an extended pre-cooler with two (or more, as appropriate) sub-sections is adopted. This embodiment is particularly useful for very low dew-point gas dehydration applications. In such a case, the gas temperature drop across the pre-cooler would be so large that the last sub-section of the pre-cooler is actually functioning as a part of the deep-cooling chiller. The following special measures are taken to avoid unacceptable rapid clogging of the flow channels in the primary side of the last sub-section of the pre-cooler.

[0030] The pre-cooler 2 is now divided into two (or more, as appropriate) sub-sections, designated as 2 a and 2 b respectively. An additional separator 5a1 and an additional water discharge pipe 4b1 are incorporated between the two sub-sections as shown. The reflux pipeline 51 is also extended to cover two reflux inlets 3 a and 3 b. The flow rates of the reflux gas are appropriately divided between the two inlets to reduce the cold gas flow in the upper (last) sub-section of the pre-cooler. The solid deposition rate in the upper sub-section, therefore, is reduced. An alternative approach to mitigate the clogging problem is to design the pre-cooler such that the heat transfer coefficients of the upper sub-section is lower than that of the lower sub-section. In a finned-plate type pre-cooler, a combination of the above-mentioned measures could be adopted.

[0031] All other features and operations in the embodiment in FIG. 3 are identical to those already described in FIG. 1. The respective flow paths of the gas and the refrigerant are shown by the respective dotted lines with arrows indicting the directions of the flows. Since the dehydration process is identical with FIG. 1, no further detailed description needs to be repeated.

[0032] The embodiment in FIG. 3 is able to deeply pre-cool the inlet gas and dehydrate the gas to a very low dew-point with minimum energy consumption.

[0033] In summary, the present invention provides an integrated gas dehydrator comprising a single integrated dehydrator processing unit and a refrigeration unit for efficient and cost-effective removal of moisture in a variety of gases, in particular the NG.

[0034] Having describes the present invention and preferable embodiments thereof, it will be recognized that numerous variations, substitutions and additions may be made to the present invention by those ordinary skills without departing from the spirit and scope of the appended claims. 

1. An integrated dehydrator processing unit comprising: a pre-cooler; a transition section; a chiller; the above sections are arranged in tandem, i.e., in an end-to-end configuration; a gas-liquid/solid particle separator incorporated between the pre-cooler and the transition section, as appropriate; a gas-liquid/solid particle separator incorporated between the transition section and the chiller, as appropriate; a final gas-liquid/solid particle separator connected to the exit end of the chiller; a water discharge pipe connected to each of the relevant gas-liquid/solid particle separators; a reflux gas pipeline connects the final separator and the pre-cooler; a gas inlet and a gas outlet pipe; and a refrigerant inlet and a refrigerant outlet pipe.
 2. An integrated dehydrator processing unit comprising: one or a pair of pre-coolers; one or a pair of transition sections; a chiller; the above sections are arranged in a side-to-side configuration; a gas-liquid/solid particle separator incorporated between the pre-cooler and the transition section, as appropriate; a gas-liquid/solid particle separator incorporated between the transition section and the chillers, as appropriate; a final gas-liquid/solid particle separator connected to the exit end of the chiller; a water discharge pipe connected to each of the relevant gas-liquid/solid particle separators; a pair of reflux openings connects the final separator and the pair of pre-coolers respectively; a pair of gas inlets and a gas outlet pipes; and a refrigerant inlet and a refrigerant outlet pipe.
 3. An integrated dehydrator processing unit according to claim 1 and 2 wherein the pre-cooler comprises a multiplicity of sub-sections.
 4. An integrated dehydrator processing unit according to claim 1 and 2 wherein the pre-cooler comprises a multiplicity of sub-sections with different heat transfer coefficients.
 5. An integrated dehydrator processing unit according to claim 1 and 2 wherein the pre-cooler comprises a multiplicity of sub-sections with a gas-liquid/solid particle separator and an associated water discharge pipe between every two adjacent sub-sections.
 6. An integrated dehydrator processing unit according to claim 1 and 2 wherein the pre-cooler comprises a multiplicity of sub-sections with a reflux gas inlet for each sub-section.
 7. An integrated dehydrator processing unit according to claim 1 or 2 and wherein the required refrigeration is provided with an industrial refrigerator.
 8. An integrated dehydrator processing unit according to claim 1 and 2 wherein the required refrigeration is provided with a gas expander/compressor unit. 